1. Field of the Invention
The present invention relates to the control of deposit formation in engines lubricated with lubricating oils by the use of additives.
2. Description of the Related Art
Ionic liquids which are low melting point salts comprising an anion and a cation have been of interest for lubrication applications because of their nonvolatility, nonflammability and thermal, mechanical and electrochemical stability.
US2007/0027038 is directed to a lubricant comprising, as the base oil, an ionic liquid formed of an anion and a cation and having an ion concentration of 1 mol/dm3 or more. In describing the ionic liquids as base oils per se, the reference goes into extensive detail in discussing the anion and cation components, and indicates the need for the ionic liquid system to be substantially water-free to avoid undesirable corrosivity and loss in viscosity. The reference identifies imidazolium, pyridinium, alkylammonium among others as suitable, useful cations and BF4− and PF6− among numerous suitable anions. Materials such as alkylpyridinium hexafluorophosphate, alkylammonium tetrafluoroborate, among others are disclosed as being suitable for use as lubricating base fluids per se. Any of the ionic liquids embraced by the reference can be used in combination with various additives and may also be used in combination with mineral oils and synthetic oils. The reference goes on to recite that the “physical properties of ionic liquids are difficult to predict from the molecular structure thereof, and properties such as viscosity, viscosity index and pour point cannot readily be controlled through modification of the molecular structure.” (Para. [0007].)
U.S. Pat. No. 4,108,858 teaches the addition of high molecular weight to N-hydrocarbyl substituted quaternary ammonium salts (hydrocarbon component molecular weight from 350 to 3000) as dispersants and detergents. The cation in '858 is high molecular weight quaternary ammonium while the anion is halide, nitrite, nitrate, carbonate, borate, alkylborate, bicarbonate, alkanoate, phosphate, alkyl phosphate, dialkyl phosphate, dialkyl dithiophosphate and the like.
U.S. 2007/0027038 teaches ionic liquids as base oils and as components which can be mixed with hydrocarbon base oils or synthetic base oils. Ionic liquids include alkylammonium salts.
U.S. Pat. No. 4,326,973 teaches quaternary ammonium succinimide salt and adds it to a 10W40 fully formulated lubricating oil where its effectiveness as a dispersant is evaluated in the Bench VC Test.
U.S. Pat. No. 4,747,971 teaches the reaction of amine-containing dispersants, such as succinimides, with fluorophosphoric acid to produce an adduct. This adduct was added to lube oil and was evaluated for its ability to passivate the dispersant against attacking fluorocarbon seals.
WO 07/055,324 teaches a synthetic lubricant comprised of a cation selected from the group consisting of imidazolium cation, pyridinium cation, quaternary ammonium cation, quaternary phosphonium cation and a bis(fluorosulfonyl)imide anion.
JP 2006/351856 is directed to ionic liquid used as lubricating oil. The ionic liquid is material of the formula:(NC)a-(A)b-X-((Q)e)-(B)c—(CN)d where X is boron, carbon, nitrogen, oxygen, aluminum, silicon, phosphorus, sulfur, arsenic or selenium, Q is an organic group, A is an integer greater than zero, and (b) to (e) are integers including zero.